Foo - Math Majors -- simplify this

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View Full Version : Math Majors -- simplify this

ManBearPig
05-21-07, 03:45 PM
If you can, please simplify this expression:

SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X))

The expression in the COS( ) looks familiar to me, but it has been 10 years since I finished my engineering degree. Thanks!

Taerom
05-21-07, 03:47 PM
42

jsharr
05-21-07, 03:50 PM
If you can, please simplify this expression:

SATAN

The expression in the COS( ) looks familiar to me, but it has been 10 years since I finished my engineering degree. Thanks!
I removed all the unnecesasry stuff and got the answer to your math problem

ManBearPig
05-21-07, 03:51 PM
Please, express the answer in terms of X and Y only; no supernatural deities.

x136
05-21-07, 03:52 PM
Who is this Y? Is she hot?

KingTermite
05-21-07, 03:58 PM
42
+1

ManBearPig
05-21-07, 04:09 PM
This ain't homework. The question is directed to math majors, not math phobics. This is not an advanced problem in the grand scheme of things; I am simply rusty on my trig and algebra.

scrapmetal
05-21-07, 04:13 PM
42

what else ..... and thanks for the fish.

KingTermite
05-21-07, 04:16 PM
This ain't homework. The question is directed to math majors, not math phobics. This is not an advanced problem in the grand scheme of things; I am simply rusty on my trig and algebra.
No it's not advanced....never said it was. I'm not a math phobic by ANY stretch of the definition (I have a bachelors and masters degree in computer engineering...methinks I've taken some math courses).....I still think it looks like you are trying to get help with a homework problem.

ManBearPig
05-21-07, 04:31 PM
I am 33 yrs old; I am not doing homework; I am a BSME (UT Austin, May, 1997)....I derived this expression trigonometrically on a project I am working on, and I don't know/remember how to simplify it.

I don't remember all the trigonometric identities because I haven't worked with them for a long while, e.g.

http://www.sosmath.com/trig/Trig5/trig5/trig5.html

CdCf
05-21-07, 04:40 PM
42

+1

43! :D :D :D

I don't think I could simplify it further myself, but I'm not very good at math anyway. Why can't you use it as it is?

ManBearPig
05-21-07, 04:47 PM
I guess I could - but if there were a generally known trigonometric identity in the field, it might look dumb for me to express it in an unnecessarily complicated fashion (e.g., to make something up, suppose everythinig in the parantheses could be replaced by cos(x/y) or something simple like that).

KingTermite
05-21-07, 04:49 PM
I am 33 yrs old; I am not doing homework; I am a BSME (UT Austin, May, 1997)....I derived this expression trigonometrically on a project I am working on, and I don't know/remember how to simplify it.

I don't remember all the trigonometric identities because I haven't worked with them for a long while, e.g.

http://www.sosmath.com/trig/Trig5/trig5/trig5.html
I'm only calling it how it looked. See it from "our" point of view. Too many kids come on here and try to get help with their homework....quite often. It would be good for you to explain your situation so we don't think (like I did) that you are a 16 year old looking for homework help. I'm sorry if I offended....but that sure is how it looked.

mtnbk3000
05-21-07, 04:56 PM
what else ..... and thanks for the fish.
whats up with people and hitchikers guide to the galaxy

lyeinyoureye
05-21-07, 05:10 PM
If you actually have a BSME, then you should now how to do this as a matter of course imo. Nothing scares me more than engineering majors that don't know their shiz, because it's an applied skill. Unlike something like english, or even pure math, where screw ups can result in poor marks or scathing peer reviews, but shiz can't really go that bad from a practical perspective. Heh, ManBearPig.

EJ123
05-21-07, 05:43 PM

Tom Stormcrowe
05-21-07, 05:44 PM
If you can, please simplify this expression:

SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X))

The expression in the COS( ) looks familiar to me, but it has been 10 years since I finished my engineering degree. Thanks!
(X±Y)1/2*COS[45-ATANG(Y/X)]
=(X±Y)(X±Y)(COS)(45-X/Y)?

I think that's how it would factor out.

j-dowsett
05-22-07, 04:52 AM
It'll give you the length of the vector from the origin to (x,y) projected onto the line x = y.

Though that might be how you derived it in the first place! Simplifying it?
Hmm, thinking dot product could be useful, (also thinking as typing so bear with me).

(x,y).(0.707, 0.707) = 0.707x + 0.707y

excel confirms.
where 0.707 is actually meant to be 1/sqrt(2)

Possible complications outside of the range 0-90 degrees due to the atan not being unique. Can't be bothered to think that hard though.

Apologies to those arguing the poster should have solved it themselves. But I needed some mental exercise due to having been laid up in hospital for four weeks avoiding my maths lectures.

edit:

Just managed it properly too.
let sqrt() denote SQRT(X^2 + Y^2) for easy writing.

SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X))

=sqrt() * [ cos(45)*cos(atan(y/x) + sin(45)*sin(atan(y/x)]
=sqrt() * [ 0.707 * x / sqrt() + 0.707 * y / sqrt() ]
=0.707 * (x + y)

ManBearPig
05-24-07, 09:03 PM
It'll give you the length of the vector from the origin to (x,y) projected onto the line x = y.

Though that might be how you derived it in the first place! Simplifying it?
Hmm, thinking dot product could be useful, (also thinking as typing so bear with me).

(x,y).(0.707, 0.707) = 0.707x + 0.707y

excel confirms.
where 0.707 is actually meant to be 1/sqrt(2)

Possible complications outside of the range 0-90 degrees due to the atan not being unique. Can't be bothered to think that hard though.

Apologies to those arguing the poster should have solved it themselves. But I needed some mental exercise due to having been laid up in hospital for four weeks avoiding my maths lectures.

edit:

Just managed it properly too.
let sqrt() denote SQRT(X^2 + Y^2) for easy writing.

SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X))

=sqrt() * [ cos(45)*cos(atan(y/x) + sin(45)*sin(atan(y/x)]
=sqrt() * [ 0.707 * x / sqrt() + 0.707 * y / sqrt() ]
=0.707 * (x + y)

Thanks, man. I actually logged in because I found the answer on my own and wanted to post it. The result I found was (X+Y) / SQRT(2). Soooooo simple. I found the answer numerically, plugging in numbers into a table and playing around with them.

Nicodemus
05-25-07, 06:06 AM
ouch. math. I mean, I love it and all but I've done my time. University flashbacks :eek:

joeprim
05-25-07, 10:04 AM
If you can, please simplify this expression:

SQRT(X^2 + Y^2) * COS(45 - ATAN(Y/X))

The expression in the COS( ) looks familiar to me, but it has been 10 years since I finished my engineering degree. Thanks!

Where are you trying to get to? The Atan will give you and angle that you then subtract from 45° get the Cos of that ...
So as long as you know x&y things should be ok. Or are you trying to use this to determine x&y?

Joe

junkyard
05-25-07, 08:43 PM
42
4*2
8

Tom Stormcrowe
05-25-07, 09:07 PM
Where are you trying to get to? The Atan will give you and angle that you then subtract from 45° get the Cos of that ...
So as long as you know x&y things should be ok. Or are you trying to use this to determine x&y?

Joe
I have no idea, I got lost at that point! :p